Affective disorders are thought to result from an interaction of biological predisposition or vulnerability and psychosocial stress. The purpose of this project is to test prospectively whether a biological vulnerability model based on platelet monoamine oxidase (MAO) activity and cortical evoked potential (EP) patterns can predict depressive episodes and to determine the extent to which psychosocial stress factors (childhood loss, life events, social support, cognitive distortion, lack of social skills, and feelings of helplessness) enhance this predictive power. On the basis of previous research, specific combinations of MAO and EP are predicted to be associated with risk of depressive episodes. Subjects in this study will be offspring of hospitalized depressed patients. The offspring and their hospitalized parent will be assessed on the biological and psychosocial measures and evaluated according to the Diagnostic Interview Schedule (DIS) and DSM-III. The Depue General Behavior Inventory and the Beck Depression Scale will be used as well. At one and two-year follow ups, the offspring and their ill parents will be re-examined clinically as well as on the biological and the psychosocial variables to determine whether any combinations predict depressive episodes. If the effect of psychosocial stress is influenced by biological factors, interventions which seek to modify psychosocial risk factors could be targeted more precisely by the use of biological screening procedures, hence more likely to be successful and cost-effective.